1. Field of the Invention
The present invention relates to a television broadcast receiver, and more particularly to a television broadcast receiver capable of receiving radio waves broadcast from broadcast stations located in many different directions.
2. Description of the Related Art
A television broadcast receiver connected to a multi-directional antenna having multiple receiving directions is known to be able to change an active receiving direction so as to receive television broadcasts from broadcast stations (transmission towers) in many directions. Such television broadcast receiver can receive television broadcasts even in an environment that many broadcast stations (transmission towers) spread around the television broadcast receiver or receiving location as in the North American Continent.
For using the television broadcast receiver, a channel registration as will be described below is made before the initial viewing after the television broadcast receiver is purchased. Normally, maximum channels (receiving frequencies) receivable or selectable at each receiving location are stored in advance in the television broadcast receiver. Thus, in the mode of channel registration, the television broadcast receiver sequentially changes the channels automatically, and further changes, for each channel, an active receiving direction of the multi-directional antenna connected to the television broadcast receiver.
Based on comparison of signal intensities received by the antenna for each channel, for example, the television broadcast receiver determines a best receiving direction of the antenna for the each channel to enable best receiving condition among the multiple receiving directions, and registers (stores) the best receiving direction in a channel information table by associating the best receiving direction with the each channel. In the present specification, this function of the television broadcast receiver is referred to as all-channel omni-directional scanning function, in which the term “all-channel” indicates that all the channels are sequentially changed to make analysis about each channel, and the term “omni-directional” indicates that active receiving direction each for the respective channels are sequentially changed to make analysis about each receiving direction in the each channel.
When a user selects a channel to view, the television broadcast receiver references a channel information table created at the time of the channel registration as described above, and makes active the best receiving direction registered in the channel information table for the channel selected by the user, thereby obtaining best receiving condition. In this way, the channel registration is normally sufficient for television viewing in good receiving condition. However, the mere channel registration sometimes is not sufficient, considering that after the channel registration, broadcast wave conditions may vary from those at the time of the channel registration as will be described below.
An important factor to be considered is time zone dependency. Depending on time zones of television broadcasts, intensities of radio waves of television broadcast signals (terrestrial waves) may vary. In some time zones, broadcasts may even be interrupted. Accordingly, channels receivable or selectable by even a stationary home television broadcast receiver may vary depending on time zones. For example, if a channel registration happens to be made in a midnight time zone for a channel of a broadcast station which broadcasts in daytime, not at midnight, the channel of the broadcast station cannot be registered in a channel information table even though the broadcast itself from the broadcast station exists. This causes a trouble that the channel of the broadcast station cannot be selected by normal channel selection on the basis of the channel information table.
In order to avoid this trouble, it can be considered to make a channel registration in the afternoon of a day which is generally not a broadcast interruption time zone. However, if the television broadcast receiver is located in e.g. a mountainous area where intensities of radio waves of television broadcast signals (terrestrial waves) are likely to be low, and if the channel registration is made for a channel of a broadcast station in a time zone when the intensity of the radio wave of the channel of the broadcast station happens to be low, the channel of the broadcast station still cannot be registered in the channel information table.
The following is a typical example of a consequence of such trouble. Assume for example that three broadcast stations A, B and C are positioned around a receiving location at which a television broadcast receiver is positioned. Further assume that an initial channel registration is made in a time zone at which received television broadcast signals of the two channels of broadcast stations A and B show effective or sufficiently high signal intensities so that the two channels are registered in the channel information table, whereas a received television broadcast signal of the channel of broadcast station C shows too low signal intensity to allow the channel to be registered in the channel information table. Still further assume that a user wishing to view television broadcast of the channel of broadcast station C commands a subsequent channel registration in a different time zone after the initial channel registration.
A conventional television broadcast receiver, when used to make the channel registrations as described above, creates a new channel information table, each time the television broadcast receiver creates a channel information table for a channel registration. Accordingly, if the signal intensity of the channel of broadcast station A happens to be too low at the subsequent channel registration, the channel of broadcast station A is not registered (stored) in the channel information table, which thus lacks the channel of broadcast station A, although the channels of broadcast stations B and C are registered in the channel information table.
In order to avoid the trouble as described above, it can be considered to partially retain data in a channel information table or tables created previously or in the past. More specifically, it is possible not to completely delete data in each channel information table created in each previous channel information registration at the time of creating a new channel registration. For example, it is possible to allow each new channel information table to retain, and thereby use, data (data of best receiving direction) for each channel once registered as a receivable or selectable channel in each channel information table created previously or in the past. However, this causes a problem described below.
In television broadcasts, not only the intensity of a radio wave or signal intensity varies depending on time zones, but also the direction from which the radio wave comes may vary with time. For example, a building which is being built around the television broadcast receiver, i.e. receiving location, may influence to change a best receiving direction. In this case, it is apparent that better receiving condition can be obtained in a best receiving direction determined by a newest channel registration than in a best receiving direction determined by a previous or past channel registration. This leads to a problem that the above-described conventional method of simply or merely using previous or past data (data of best receiving direction), as is, for a channel determined to be a selectable channel cannot fully utilize the omni-directional function performed at the time of channel registration, preventing a user from viewing television broadcast of such channel in best receiving condition.
Another example of antenna technology is used in a television broadcast receiver mounted on an automobile for the purpose of enabling good receiving condition in an environment where broadcast wave conditions vary. Since an automobile and hence receiving location moves, receivable broadcast stations change as it moves. Japanese Laid-open Patent Publication Hei 8-97680 discloses a television broadcast receiver to enable secure setting of such changing broadcast stations. The television broadcast receiver of this Patent Publication stores therein an information table in advance about information of receivable broadcast stations based on latitudinal and longitudinal positions of the broadcast stations. The television broadcast receiver obtains data of current position of the automobile from a GPS (Global Positioning System) receiver mounted on the automobile, and references the information table with the data of current position so as to acquire data of receivable broadcast stations at the current position. Based on the data of the receivable broadcast stations, the television broadcast receiver performs an all-channel scanning function so as to make it possible to set all receivable channels at the current position without a miss. However, this technology does not detect receiving condition in each receiving direction so as to control reception of a television broadcast signal according to the receiving condition.